Firefighters, members of Verdi union, march during a strike near Frankfurt airport, Germany, April 27, 2016. The strike by workers, including ground services, security checks, fire fighting and check-in staff, are likely to severely impede operations at German airports and airport operator Fraport has warned it could take a day or two for services to return to normal. The banner reads 'Invest in the future now'. REUTERS/Kai Pfaffenbach